1. Field of the Invention
This invention relates generally to stripping compositions to remove polymer coatings from electronic components and, more particularly, to a stripping composition that removes polyimide coatings from semiconductor integrated circuit devices for rework of the device without damaging the underlying metal circuitry of the device. In one particular application, a cured polyimide used as a top seal of an integrated circuit chip module is removed for rework using a method employing the stripping composition of the invention.
2. Description of Related Art
The manufacture of semiconductor integrated circuits typically involves highly complex, time-consuming and costly processes which, with continually narrower line width requirements, must be achieved with an ever increasing degree of precision. During the manufacture of the semiconductor and semiconductor microcircuits, it is necessary to coat the substrates from which the semiconductors and microcircuits are made with a polymeric organic film, generally referred to as a photoresist, e.g., a substance which forms a patterned image upon exposure to light and developing. These type photoresists are used to protect selected areas of the surface of the substrate while a process such as etching is used to selectively modify materials at unprotected areas of the substrate.
In the manufacture of integrated circuits, the process steps include coating onto the surfaces of semiconductor substrates materials such as metals to define the circuitry, dielectrics as insulators and organic polymeric materials to protect the circuit patterns in the electronic component. The substrate is typically an SiO.sub.2 dielectric covered silicon wafer and contains metallic microcircuitry such as aluminum or aluminum alloys in and/or on the dielectric surface.
Basically, the fabrication of integrated circuits utilizes a photoresist composition which generally comprises a polymeric resin, a radiation sensitive compound and a suitable solvent to enable forming a film of the photoresist over a particular substrate for photolithographically delineating patterns on such substrates. In a typical processing scheme, the photoresist compositions are spun on or applied to the substrate using methods known in the art. Then the photoresist compositions are typically subjected to a pre-exposure bake to drive off a portion of the solvent to impart dimensional stability to the film. The coated substrate is selectively exposed with radiation such as UV, e-beam or x-ray spectra through a patterning mask using an appropriate exposure tool for such exposure. After exposure, the coated substrate undergoes a development process where, due to selective dissolution of certain areas, a pattern is formed or developed. In certain areas of the photoresist film, the photoresist material is completely removed whereas in the other areas the remaining photoresist forms a pattern having a desired or intended configuration. Such patterns are used to mask or protect the substrate for subsequent wet or dry etching processes, the deposit of conductor or insulative patterns, or for incorporation of the pattern photoresist into the device or package as, for example, an insulating or dielectric layer.
In one fabrication process for an integrated circuit, a top coating can be applied to the integrated circuit. Typically, a polymer layer is applied to the top surface of the integrated circuit and developed to expose pads on the surface of the integrated circuit device. The polymer is then cured and an interconnect is made through the surface of the integrated circuit device.
Polyimides are increasingly being used in integrated circuit manufacture. The use of a polyimide as a fabrication aid includes application of the polyimide as a photoresist, planarization layer and insulator. In these applications, the polymers are applied to a wafer substrate and subsequently cured in the desired pattern by a suitable method. When the polyimide is used as a seal or a top coat, the polyimide layer is not removed except for the areas over the pads and remains on the surface of the semiconductor device.
Semiconductor devices are very expensive and if there is a defect in the device, it is highly desirable to be able to repair the device. To repair (typically termed "rework") the device, it is necessary to remove coatings such as polyimides, epoxies and the like and it is essential that the underlying metallization of the device not be adversely affected by the stripping composition.